This invention relates to direct bonding of optical components. More particularly, the invention relates to methods for direct bonding of optical components using a low temperature process without the use of adhesives to form a bond between the components.
Bonding of optical waveguide fibers to photonic or optical components such as a second optical waveguide fiber, a lens or lens arrays typically utilizes fusion bonding, adhesive bonding or mechanical mounting with an air gap to provide a bond between the optical fiber and the component. For example, optical fibers are typically spliced together using fusion bonding, wherein the fiber ends are abutted to one another and heated to their softening point to obtain a bond between the fibers. Fusion splicing may work well for two fibers having the same glass composition, however, such bonding is problematic for two or more fibers having differing compositions. As one example, fusion bonding of an antimony silicate fiber (e.g., XBLAN) with a silica-based fiber is not possible because the difference in the softening temperature of these two types of glasses is too great to allow bonding without deformation of the fiber having the lower softening point or impairment of its optical properties. Furthermore, low yields due to splice breaks result when two fibers having significantly different CTE""s are bonded together at a high temperature and then cooled to room temperature.
Wringing is another type of bonding process available for bonding and refers to a process of bonding glass surfaces in which adsorbed surface groups are removed from active bonds on a surface by heating the parts to temperatures typically above 600xc2x0 C. but below the softening point of the glass. Adsorbed water and organics will vaporize and the result is that the surface sites become xe2x80x9cactive.xe2x80x9d At such a temperature or after cooling in a clean, low humidity environment, surfaces can be placed in contact at which point covalent bonds spontaneously form between xe2x80x9cactivexe2x80x9d bonds on each surface. This is similar to vacuum bonding, except the surface is activated by temperature rather than by a strong vacuum. However, neither of these processes is suitable in systems that include polymeric components, such as optical fiber coatings, because high temperatures and high vacuum pressures are detrimental to polymers.
In the manufacture of fiber-lens arrays, typically an array of optical fibers, which may comprise any number of fibers arranged in a one or two dimensional array, the fiber ends are typically bonded to the lens array by either adhesive bonding or mechanical mounting at a predetermined distance from the lens array with an air gap. The use of adhesive bonding, however, does not provide a clear optical path between the endface of the fibers and the individual lens elements in the lens array. A disadvantage of mechanical mounting is that an air gap is present between the bonded surfaces. Since this air gap has a different refractive index from the fiber and the lens, an antireflective coating must be applied to both surfaces to minimize losses. In cases in which the refractive index of the fiber and the lens is the same, an index matching material, such as an oil, can be placed in the gap between the fiber and the lens. Index matching materials and adhesives, however, are not reliable, particularly when the bonded parts encounter thermal cycling.
It would be desirable to provide a bonding process for optical fiber waveguides and optical components that results in an optically clear bond. In addition, it would be advantageous to bond optical fibers and components together without the use of adhesives or temperatures near the softening temperature of the optical fibers. In systems that include polymeric components, such as coatings on optical fibers, it would be desirable to provide a process that does not require temperatures that are detrimental to the polymers present in the bonded system.
One embodiment of the invention relates to a method of manufacturing an optical component. This embodiment includes the steps of providing an optical waveguide with a bonding surface, , and providing an article having a surface for bonding to the bonding surface of the optical waveguide. The article may contain silicon or glass. In another embodiment, the optical waveguide is an optical waveguide fiber and the bonding surface includes an endface of the fiber. In this embodiment, the bonding surface of the optical fiber waveguide and the surface of the article are bonded together without an adhesive and at a temperature below the softening temperature of the optical waveguide fiber, and preferably below a temperature that would degrade any polymeric coating associated with the fiber.
In one embodiment of the invention, the glass article includes a second optical waveguide fiber. In another aspect of this embodiment, the first and second optical waveguide fibers are disposed within ferrules. In still another aspect, the article may include a photonic component such as a planar waveguide, an amplifier, a filter, a prism, a polarizer, a birefringent crystal, a faraday rotator and a lens. In still another aspect, the article may include an infrared transparent material such as glass or silicon.
According to another embodiment of the invention, the bonding surface of the optical waveguide and the surface of the article may be contacted with a solution prior to bonding. In still another aspect, the solution has a pH greater than 8. Another embodiment of the invention involves providing termination groups on the bonding surface of the optical waveguide and the surface of the article. According to this aspect, the termination groups may include xe2x80x94OH, xe2x89xa1Sixe2x80x94OH, xe2x95x90Sixe2x80x94(OH)2, xe2x80x94Sixe2x80x94(OH)3 and xe2x80x94Oxe2x80x94Sixe2x80x94(OH)3, and combinations thereof.
Still another embodiment of the invention may include the step of providing a hydrophilic surface on the bonding surface of the optical waveguide and the surface of the article. This embodiment may include forming hydrogen bonds between the bonding surface of the optical waveguide and the surface of the article. This may be accomplished by contacting the bonding surface of the optical waveguide and the surface of the article with an acid. It may also be desirable to contact the bonding surface of the optical waveguide and the surface of the article with a solution having a pH greater than 8. Such a solution may include a hydroxide such as sodium hydroxide, potassium hydroxide or ammonium hydroxide. Another embodiment of the invention may involve eliminating absorbed water molecules at the interface between the bonding surface of the optical waveguide and surface of the article, which may be accomplished by heating the interface.
According to another embodiment of the invention, a method of bonding a lens array to an optical waveguide array is provided. In this aspect, an array of optical waveguides, for example, waveguide fibers having bonding surfaces, is provided and aligned with a lens array having surfaces for bonding to the bonding surfaces of the optical waveguide fibers. The surfaces of the lens array are placed in contact with the bonding surfaces of the optical waveguide fibers in the absence of an adhesive and below the softening temperature of the optical waveguide fibers, preferably below a temperature that would degrade any polymeric coatings on the fiber, to bond the fibers and the lenses together. As in the previous embodiment, bonding may be achieved by contacting the bonding surface of the optical waveguide fibers and the surfaces of the lens array with a solution, preferably a solution having a pH greater than 8. Another embodiment may involve providing termination groups on the bonding surfaces of the optical waveguide fibers and the surfaces of lens array. The termination groups may include xe2x80x94OH, xe2x89xa1Sixe2x80x94OH, xe2x95x90Sixe2x80x94(OH)2, xe2x80x94Sixe2x80x94(OH)3 and xe2x80x94Oxe2x80x94Sixe2x80x94(OH)3, and combinations thereof. Bonding of the lens array with the fiber array may further include forming hydrogen bonds between the bonding surfaces of the optical fibers and the surfaces of the lens array. This may be accomplished by contacting the bonding surface of the optical waveguide fibers and the surfaces of the lens array with an acid. The bonding method may further involve eliminating absorbed water molecules and adsorbed hydroxyl groups at the interface between the bonding surface of the optical fiber waveguide and surfaces of the lens array, which may be achieved by heating the interface. In another aspect, it may be desirable to dry the surfaces to remove absorbed water molecules and to draw a slight vacuum, for example, about 10xe2x88x923 millibar, to assist in the prevention of an air gap between the surfaces. In still another embodiment, the optical fibers are disposed in a frame including a bonding surface and the lenses are disposed in a frame including a bonding surface, and the bonding surface of the lens frame and the bonding surface of the fiber frame are placed in contact to bond the frames together.
Still another embodiment of the invention relates to manufacturing an optical component including the steps of providing two optical articles each having a bonding surface and bonding the surface of the respective articles to each other without an adhesive and at a softening temperature below the optical article. The optical articles may include, but are not limited to a lens, a prism, a polarizer, a grating, a filter, a birefringent crystal, and a faraday rotator. One aspect of this embodiment involves contacting the optical articles with a solution, for example, a solution having a pH greater than 8, such as sodium hydroxide. As in the previously described embodiments, further aspects may include providing termination groups and/or providing a hydrophilic surfaces on the bonding surfaces of the optical articles.
The invention provides a simple, low temperature and reliable bonding method that provides an optically clear bond between optical fibers and optical components. Bonding can occur at temperatures lower than the softening or deformation temperature of the glass, and in some cases lower than 100xc2x0 C. Additional advantages of the invention will be set forth in the following detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed.